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Question number: 28

Question

A black body is at a temperature of 2550 K. The energy of radiation emitted by this object with wavelength between 499 nm and 500 nm is U1 between 999 nm and 1000 nm is U2 and between 1499 nm and 1500 nm is U3. The Wein’s constant b = 2.88 × 10 6 nm K. Then

Choices

Choice (4)

Response

a.

Equation

b.

Equation

c.

Equation

d.

Equation

Question number: 29

Question

A 5 cm thick ice block is there on the surface of water in a lake. The temperature of air is - 10° C; how much time it will take to double the thickness of the block (L = 80 cal/g, Kice = 0.004 erg/s-k, dice = 0.92 g cm -3)

Choices

Choice (4)

Response

a.

191 hours

b.

1 hour

c.

1.91 hours

d.

19.1 hours

Question number: 30

Question

Consider two hot bodies B1 and B 2 which have temperature 100° C and 60° C respectively at t = 0. The temperature of surroundings is 50° C. The ratio of the respective rates of cooling R 1 and R 2 of these two bodies at t = 0 will be

Choices

Choice (4)

Response

a.

R 1: R 2 = 4: 5

b.

R 1: R 2 = 3: 2

c.

R 1: R 2 = 2: 3

d.

R 1: R 2 = 5: 1

Question number: 31

Question

A composite metal bar of uniform section is made up of length 25 cm of copper, 10 cm of nickel and 15 cm of aluminum. Each part being in perfect thermal contact with the adjoining part. The copper end of the composite rod is maintained at 100°C and the aluminum end at 0°C. The whole rod is covered with belt so that there is no heat loss occurs at the sides. If K Cu = 2Kal and Ka1 = 3K Ni, then what will be the temperatures of Cu - Ni and Ni - Al junctions respectively